Field of the Invention
This invention relates to injection apparatus, and in particular, though not exclusively, to injection apparatus designed to allow a number of doses to be delivered from a single cartridge or syringe over a period of time.
Description of the Related Art
In many therapies a drug needs to be injected at daily or other periodic intervals. A potential problem arises because the user may not recall clearly whether they have taken a particular dose. There is therefore a need in such apparatus to provide an increment counter, or day of the week indicator, which indicates whether they have taken the dose for a particular period. Also, where a fixed volume dose is delivered each time, it is highly desirable to be able to signal to the user when all useable doses have been taken from the device to prevent a user from inadvertently taking a nil or incomplete dose. Although it is common on variable dose devices to provide a counter display to allow a user to dial in the number of units of medicament they wish to inject, these displays only indicate the magnitude of the dose to be delivered, and return to zero on completion of an injection. They do not indicate a dose application count i.e. the accumulated number of injections that have been performed by the device.
In EP-A-1463550, we describe a dose application counter for an injection device having a dose counter member which has a lost motion connection to the dose setting element, so that, as a user sets the amount of the dosage volume prior to firing the device, the dose application counter is incremented by one count, irrespective of the number of units making up the dose. Although this is a good design, it increments the count on setting of the dose rather than actual delivery of the dose. It is possible therefore that if a user is distracted between the setting dose and delivering it, the dose application counter suggests that the dose for that period has already been taken. Also, after the device has been fired to deliver the final available dose, the dose setting knob can still be rotated to set a further dose even though subsequent firing of the device will not deliver a proper dose.